Pro-Russian Crimeans cheered well into the night outside their regional parliament.
Some waved Russian flags and paraded a giant Russian flag through the streets.
They were celebrating an announcement made a parliament speaker who said that a referendum on whether Crimea should be independent from Ukraine will be held May 25.
That's the same day Ukraine plans to elect a new president to replace Viktor Yanukovich, who was ousted last week following deadly anti-government protests.
Crimea is the only Ukrainian region that has an ethnic Russian majority.
In Washington, U.S. Secretary of State John Kerry urged Russia to join the U.S. in helping Ukraine.
(SOUNDBITE) (English) U.S. SECRETARY OF STATE JOHN KERRY SAYING:
"This morning, I called Foreign Minister Lavrov and we talked at some length about the transition and the events in Ukraine and the region and I asked, specifically, that Russia work with the United States and with our friends and allies in order to support Ukraine to rebuild unity, security and a healthy economy."
He also urged Russia to respect the territorial integrity of Ukraine, with respect to the situation in Crimea.
White House spokesman Jay Carney also weighed in on the Ukraine crisis.
(SOUNDBITE) (English) WHITE HOUSE PRESS SECRETARY JAY CARNEY SAYING:
"We strongly support Ukraine's territorial integrity and sovereignty. We expect other nations to do the same. And so we are closely watching Russia's military exercises along the Ukrainian border, which they announced yesterday. We expect Russia to be transparent about these activities and to avoid provocative actions. We urge them not to take any steps that could be misinterpreted or lead to a miscalculation during a very delicate time."
Earlier in the day Interfax news agency and eyewitness reports said armed men seized this government building in Crimea.
There has since been no official word on who may have seized the building and it is uncertain whether they are still inside.